In many modern image display systems, image frames of an analog image signal, such as analog video, analog computer graphics, analog DVDs, analog game console output, and so forth, may be digitized prior to being displayed. Digitizing the image frames of the analog image signal may enable processing of the image frames by image processing hardware in the image display system. The processing performed by the image processing hardware may improve image quality, reduce image noise, enhance desired properties of the image, deemphasize undesired properties of the image, and so on, for example.
The digitizing may include sampling the analog image signal without prior knowledge of a sampling frequency or sampling phase using an analog to digital converter (ADC). In order to properly digitize the images in the analog image signal, a sampling frequency generally must be detected. If the sampling frequency is incorrectly detected, then when the digitized images are displayed, the resulting images may be distorted at best or completely incomprehensible at worst.
In a technique used to determine the sampling frequency, portions of the image containing high frequency content may be used to compute the sampling frequency offset or verify the sampling frequency. This technique makes use of the actual content of the image (and that of subsequent images) to determine the sampling frequency. Therefore, there may be a need to find the portions of an image containing high frequency content to expedite the determining of the sampling frequency.
FIG. 1a illustrates an image 100, wherein the image 100 contains high frequency content 105. The rapidly changing, high contrast, high frequency content 105 may enable the use of the actual content of the image 100 in the determining of the sampling frequency. FIG. 1b illustrates an image 120, wherein the image 120 contains no high frequency content.
FIG. 1c illustrates an image 140, wherein the image 140 contains content that includes some high frequency information, such as line 145 and line 146. However, since processing of the image 140 to determine sampling frequency offset generally requires vertically oriented high frequency data, the lines 145-146 may not include sufficient high frequency information to enable the determining of the sampling frequency offset.
FIG. 2a illustrates an image, such as an image 200, wherein the image 200 includes a portion 205 containing high frequency content. Because an image may or may not contain high frequency content and, if an image contains high frequency content, the high frequency content's location in the image may vary from frame to frame in an image sequence, it may be necessary to locate the high frequency content on an individual image by image basis.
FIGS. 2b through 2d illustrate a technique for locating the portion 205 of the image 200. A binary search may be used to locate the portion 205 of the image 200. Binary search techniques offer shorter than linear search times, which may be important, because finding high frequency content may be crucial in determining a sampling frequency that may be used in displaying the image 200.
FIG. 2b illustrates the image 200, wherein the image 200 has been partitioned into two halves, a first half 220 and a second half 225. The two halves are approximately the same size and divide the image 200 horizontally into two. A check may then be made of each of the two halves to determine if either of the halves contains high frequency content (the portion 205). The check determines that the first half 220 contains the high frequency content and the second half 225 does not, so the second half 225 may be eliminated from subsequent searches.
FIG. 2c illustrates the image 200, wherein the image 200 has been partitioned into two quarters, a first quarter 240 and a second quarter 245. The quarters are partitioned from the first half 220. A check may then be made of each of the two quarters to determine if either of the quarters contains high frequency content. The check determines that the second quarter 245 contains the high frequency content and the first quarter 240 does not, so the first quarter 240 may be eliminated from subsequent searches.
FIG. 2d illustrates the image 200, highlighting the second quarter 245, which contains the high frequency content. The second quarter 245 of the image 200 and of subsequent images may then be used to determine the sampling frequency of the image 200. By providing a percentage of the image 200, rather than the entire image 200, the determining of the sampling frequency may potentially be accelerated. Furthermore, the use of a part of the image 200 instead of the entire image 200 may enable the use of a smaller memory, which may help to reduce the overall cost and complexity of an electronic device making use of the image 200.
FIG. 3 illustrates an electronic device 300 that includes a memory 305 that may not be capable of simultaneously storing the image 200 in its entirety. In such a situation, if the electronic device 300 requires that the entire image 200 be used in determining the sampling frequency, then different parts of the image 200 may need to be moved into the memory 305 while the sampling frequency is being determined. This may complicate and slow down the determining of the sampling frequency. However, if the electronic device 300 may require only a part of the image 200 that contains high frequency content, then only the part of the image 200 containing the high frequency content, wherein the size of the part may correspond to the size of the memory 305, may be provided to the electronic device 300.